1. Field of the Invention
The present invention relates to a vibration motor including a weight secured to a core.
2. Description of the Related Art
Hitherto, Japanese Unexamined Patent Application Publication No. 2002-219411 exists as a document that describes a technology of such a field. A weight used in a vibration motor discussed in this document includes a columnar body and a projecting portion formed at one end of the body. The shape of the body in cross section corresponds to the shape of a space, that is, a core slot formed between two coil winding portions of a core. When the body of the weight is inserted in the core slot, the body of the weight closely contacts surfaces of coils and inner surfaces of tooth portions at end portions of the coil winding portions, so that the position of the body of the weight is restricted in a plane that is perpendicular to an axial direction. Further, the position of the weight in the axial direction is restricted by contact of the projecting portion with surfaces of the tooth portions of the coil winding portions at a final stage of the insertion of the weight. The weight inserted in this way is secured by laser welding to a boundary region between a portion of the weight that is exposed to the outside and the tooth portions of the coil winding portions.
In the above-described vibration motor of the related art, the weight closely contacts the surfaces of the coils and the inner surfaces of the tooth portions at the end portions of the coil winding portions, so that the position of the weight in a plane that is perpendicular to the axial direction is restricted. This prevents the weight from falling towards an inner side in the core slot. However, since, when the weight is installed in the vibration motor or the vibration motor is used, the weight contacts the coils, the coils may break. In addition, when, in order to prevent the coils from breaking, the weight is formed with a size that does not allow the surfaces of the coils to contact the weight, that is, the weight is reduced in size, the weight tends to fall towards the inner side in the core slot when the weight is being installed in the vibration motor. Therefore, laser welding tends to be improperly performed when securing the weight to the tooth portions of the coil winding portions. Further, since, when using the vibration motor, a force acting radially inward upon the weight is only supported by the weld, an unreasonable force continues to act upon the welded portion. This may gradually reduce the securing strength of the weight.
Japanese Unexamined Patent Application Publication No. 2003-164804 is another example of a related art.